The present invention relates to an image sensing apparatus and method using a solid-state image sensing device, such as CCD, and more particularly, to an image sensing apparatus and method realizing high-resolution image sensing by using "pixel shifting technique" and a method of dealing with obtained data of the plurality of images sensed by using the pixel shifting technique.
Conventionally, there are the following methods for increasing image sensing resolution adopted by an image sensing apparatus using a solid-state image sensing device.
(a). Increase the density of pixels in the image sensing device. PA1 (b). Use a plurality of image sensing devices. PA1 (c). Use pixel shifting technique.
Regarding method (a), the method greatly depends upon semiconductor manufacturing technique, thus it does not improve quickly. Further, although the semiconductor manufacturing technique improves, the price of the image sensing device will increase. Regarding method (b), it can be realized relatively easily by using an optical prism, or the like. However, three image sensing devices as well as a large optical member, such as the optical prism, for separating incoming light into three color components which travel different paths from each other are necessary. As a result, the cost for manufacturing an image sensing apparatus increases.
Because of the problems of using methods (a) and (b), method (c), namely pixel shifting technique, has been used for realizing high-resolution image sensing. The pixel shifting technique is that a plurality of images of an object are sensed as shifting image formation positions on the image sensing device, and combined to produce a single high-resolution still image. This technique is disclosed in the Japanese Patent Publication No. 50-17134, for example.
As for pixel shifting technique using a single image sensing device, the one disclosed in the Japanese Patent Publication No. 1-863 is known. This discloses a technique to obtain a plurality of images sensed by moving an optical system, image sensing device or an object by a predetermined amount, then combine the obtained plurality of images to produce a single image of high resolution.
However, in the aforementioned conventional pixel shifting techniques, only basic techniques are suggested. Especially, when the pixel shifting is performed by using a single image sensing device, since a color filter is attached, no concrete way of shifting pixels has been described. Furthermore, there were no description on data handling, such as how color processes are performed on obtained image data and whether the high resolution still image sensing is performed while sensing a moving image or not, which have been problems upon developing an image sensing apparatus in practice.
Further, it is possible to obtain images of different resolution depending upon how the pixels are shifted, however, there was no suggestion to change the ways of shifting pixels in accordance with characteristics of the object.
Furthermore, the image sensing apparatus using a solid-state image sensing device focuses on the object, measures light exposure, and adjusts white balance for each sensed image. However, focusing on the object, measurement of light exposure, and correction of white balance have not been exclusively considered for the pixel shifting technique in which a plurality of images are sensed by shifting the relative positions between the image sensing device and the object in the horizontal direction, vertical direction and oblique direction, and combined into a single image of high quality.
In a case of sensing a plurality of images needed for producing a combined high resolution image by using the pixel shifting technique, still life, a stationary object, is generally sensed in most of the cases, and conditions for sensing the images seldom change. Thus, if the focusing on the object, measurement of light exposure, and white balance correction are performed each time when sensing an image of the object to be used for generating a single image of high resolution, errors in measurement and in operation of each detection device may result in changing conditions for sensing the images, thereby making it difficult to combine the plurality of obtained images into a single image of high resolution.
Further, for performing the focusing on the object, measurement of light exposure and white balance correction for each image sensing operation, it is necessary to operate driving circuits. Therefore, time as well as energy of a battery are wasted.